1. Field of the Invention
The present invention relates to an auxiliary lock of the type having an interchangeable lock core with improved pull-resistant structure to prevent the lock core from being forcibly pulled outwards.
2. Description of the Related Art
Auxiliary locks provide additional protection to property and life. Auxiliary locks generally includes three types, i.e., "blank plate type" in which the auxiliary lock can be locked or unlocked by a key from outside only, "single cylinder type" in which the auxiliary lock can be locked or unlocked by a key from outside and by a thumbturn on the inside, and "double cylinder type" in which the auxiliary lock can be locked or unlocked by a key from either side.
FIG. 5 of the drawings illustrates a conventional auxiliary lock 60 of single cylinder type. A lock core housing 70 is mounted in a positioning seat 62, which, in turn, is mounted in a housing 61. Removably mounted in a figure "8" compartment 71 of the lock core housing 70 is a lock core 80 that is also substantially "8" shaped. As shown in FIG. 6, the lock core 80 includes a recessed section 81 in each of two lateral sides thereof, wherein one of the recessed sections 81 has a core lug 82 movably received therein. A lateral inner wall that defines a portion of the figure "8" compartment 71 of the lock core housing 70 includes a protruded edge 72. When the lock core 80 is inserted into the compartment 71 and the key for changing lock cores is rotated through a pre-determined angle to a position for locking/unlocking, the core lug 82 is extended outward into a space 73 behind the protruded edge 72. Thus, the lock core 80 is not removable after the key for changing lock cores is removed.
Still referring to FIG. 5, when mounted to a door 90, a tail piece 75 is connected to a thumbturn 77 located inside. In addition, the tail piece 75 is connected to an end of the lock core 80. Accordingly, the user may lock or unlock the auxiliary lock 60 by a key from outside or by the thumbturn 77 from inside.
Theoretically, when the core lug 82 of the lock core 80 is located in the space 73 behind the protruded edge 72, the lock core 80 cannot be removed unless the key for changing the lock core is inserted into a keyway 83 of the lock core 80 and rotated through a pre-determined angle, as the core lug 82 will be stopped by the protruded edge 72 if the lock core 80 is pulled longitudinally outwards. In practice, an unauthorized person still may forcibly remove the lock core 80, destroy the auxiliary lock 60, and thus open the door 90. It is found that the lock core 80 is merely retained in place by means of the core lug 82 stopped by the protruded edge 72 that has a relatively small area. An unauthorized person may drill a screw hole in the front face of the lock core 80 and then insert a T-bolt into the screw hole. Then, the unauthorized person may apply a relatively large force to pull the T-bolt outwards and thus destroy the protruded edge 72 by the core lug 82. As a result, the auxiliary lock 60 is damaged and the door 90 is no longer locked. In brief, the auxiliary locks of the type having an interchangeable lock core can be easily disabled, as the retaining effect of the core lug 82 is not enough. The present invention is intended to provide an auxiliary lock that mitigates and/or obviates this problem.